Tungsten/copper composite powders are used in the manufacture of electronic components, such as heatsinks, electrical contacts and electrodes.
Because tungsten and copper do not alloy readily, various methods have been used to combine them in order to form tungsten/copper composite bodies. For example, tungsten powder may be pressed into a desired shape and then sintered to form a porous tungsten body. Molten copper may then be infiltrated into the tungsten body by capillary action.
U.S. Pat. Nos. 3,489,530 to Schreiner, and 3,449,120, 3,440,043 and 3,467,517 to Zdanuk et al. disclose methods of making tungsten/copper composite bodies using copper infiltration methods.
The amount of copper which may be incorporated into the tungsten body is determined by the porosity of the sintered tungsten body, which depends on the particle size of the tungsten powder used and the sintering conditions. Thus, the range of tungsten/copper compositions is limited when copper infiltration methods are used. Further, although tungsten powder may be pressed and sintered to obtain near net-shape parts, the subsequent copper-infiltration step creates a need for a final machining step to obtain finished dimensions. Finally, the copper infiltration methods are only economically feasible with tungsten bodies having basic geometries, since one or more final machining steps must always be performed after copper infiltration of the tungsten body.
Another method of obtaining a tungsten/copper composite body involves the blending and co-reduction in hydrogen of tungsten oxide and copper oxide powders to obtain a tungsten/copper composite powder, which may then be pressed and sintered to obtain a tungsten/copper composite body. Co-reduction methods are labor-intensive and expensive because they require one or more additional agglomeration steps to impart flowability to the resulting powders. They also require strict control of the reducing conditions, including temperature, hydrogen gas flow rate and powder bed depth during reduction, in order to obtain the desired powder particle size. Tungsten/copper composite powders produced by co-reduction of the respective oxides are extremely fine and tend to agglomerate during subsequent processing steps, thus limiting their usefulness in the powder metallurgical manufacture of small parts.
It would be an advancement in the art to provide a method of making tungsten/copper composite powders which are flowable and thus suitable for use in standard powder metallurgical manufacturing operations. It would also be an advancement in the art to provide a method of making tungsten/copper composite powders in which a broad range of copper contents is obtainable. It would also be an advancement in the art to provide a method of making tungsten/copper composite powders which overcomes the limitations inherent in the copper-infiltration and co-reduction methods.